This invention relates to compounds used in photoresist and, more particularly, to chemically amplified photoresist sensitive to far-ultraviolet light equal in wavelength to or less than 220 nanometers, polymer used for producing the chemically amplified resist, monomer for producing the polymer and a method for transferring a pattern to a chemically amplified resist layer.
Pattern images are sequentially transferred to semiconductor wafers in processes for fabricating semiconductor devices, and design rules have been renewed in the fabrication process. Now, semiconductor devices are designed under sub-micron rules, and requirements for the photolithography get sever and sever.
Manufacturers require 0.13 micron patterns for 1 giga-bit DRAMs (Dynamic Random Access Memory), and research and development efforts are being made for the photolithography used in the ultra large scale integration. 193-nanometer wavelength ArF excimer laser lithography is disclosed by Donald C. Hofer et. al. in xe2x80x9c193 nm Photoresist R and D: The Risk and Challengexe2x80x9d, Journal of Photopolymer Science and Technology, vol. 9, No. 3, pages 387-397, 1996. The ArF excimer laser lithography requires new photo-resist. The ArF excimer laser system is expensive, and the gaseous mixture used therein is short in lifetime. In these circumstances, the new photoresist is expected to be highly sensitive to the ArF excimer laser light as well as the high resolution from the viewpoint of the cost performance.
The chemically amplified photoresist is attractive. The chemically amplified photoresist contains photo-acid generator, which accelerates the chemical reaction in the photoresist. A typical example of the chemically amplified photoresist is disclosed in Japanese Patent Application laid-open No. 2-27660. The prior art chemically amplified photoresist contains triphenylsulfonium hexafluoroarsenate and poly (p-tert-butoxycarbonyloxy-xcex1-methylstyrene). The prior art chemically amplified photoresist is presently used in KrF excimer laser lithography as taught by Hiroshi Itoh and C. Grantwillson, American Chemical Society Symposium Series, vol. 242, pages 11-23, 1984.
When the chemically amplified photoresist is exposed to the light, proton acid is generated from the photo-acid generator. The proton acid reacts with the copolymer in the heat treatment after the exposure to the light. The amount of reaction per photon, i.e., photoreaction efficiency is enhanced through the acid-catalyzed reaction. Although the photoreaction efficiency is less than 1 in the conventional photoresist, the chemically amplified photoresist achieves the photoreaction efficiency greater than 1, and most of new products of photoresist presently developed are of the type chemically amplified.
The ArF excimer laser is an example of the short-wavelength band equal to or less than 220 nanometers. The photoresist available for the photolithography in the short-wavelength band is expected to be transparent to the exposure light and large in resistance against dry etching. The prior art products of photoresist, which are responsive to g-line with 438 nanometer wavelength, i-line with 365 nanometer wavelength or KrF excimer laser light with 248 nanometer wavelength, contain copolymer having the structural unit with the aromatic ring such as novolak resin or poly (p-vinylphenol), and the aromatic ring makes the copolymer resistive against the dry etching.
Although the copolymer with the aromatic ring is preferable for the KrF excimer laser light or the long wavelength rays, the copolymer exhibits strong light absorption to the light in the short wavelength band equal to or greater than 220 nanometer wavelength. In fact, when the prior art photoresist based on the copolymer is exposed to the ArF excimer laser light, most of the ArF excimer laser light is absorbed in the surface portion of the prior art photoresist layer, and hardly reaches the substrate. This means that any fine pattern is not obtained from the prior art photoresist layer.
As described hereinbefore, the prior art products of photoresist are not available for the ArF excimer laser lithography, and the semiconductor manufacturers desire a new product of photoresist available for the ArF excimer laser lithography. The structural unit of the photoresist is expected to exhibit large resistance against dry etching without the aromatic ring, because the photoresist would exhibit the transparency to the ArF excimer laser light.
The prior art photoresist available for 193 nm ArF excimer laser lithography is taught by Takechi et. al., Journal of Photopolymer Science and Technology, vol. 5, No. 3, pages 439 to 446, 1992. The photoresist is based on copolymer having adamantyl methacrylate units which are alicylic polymer. Another prior art photoresist is based on copolymer having isobornyl methacrylate units as disclosed by R. D. Allen et. al, Journal of Photopolymer Science and Technology, vol. 8, No. 4, pages 623 to 636, 1995 and vol. 9, No. 3, pages 465-474, 1996. Yet another prior art photoresist is based on copolymer having the structural unit of alternating copolymerization between norbornene and maleic anhidride as taught by F. M. Houlihan et. al, Macro-molecues, vol. 30, pages 6517-6524, 1997.
Carboxy group and hydroxy group are categorized in the polar groups. The polar group makes the photoresist strongly held in contact with substrates, and are preferable to the photoresist. However, the aforementioned monomer, which has the alicylic group, does not have any polar group. The prior art photoresist is hydrophobic, and the photoresist layer is liable to peel off from the substrates such as silicon substrates. Thus, the first drawback inherent in the prior art photoresist is the weak adhesion to substrates.
The second drawback inherent in the photoresist containing the polymer having an alicylic group is poor uniformity of film formation. When the prior art photoresist is spread over substrates, the prior art photoresist layers are irregular in thickness. This phenomenon is also derived from the hydrophobic property due to the lack of the polar group.
The third drawback is a small difference in solubility between the pre-exposure to light and the post-exposure. Adamantyl-containing residue, isobornyl-containing residue and menthyl-containing residue give the strong resistance against dry etching to the photoresist. However, the prior art photoresist does not have any residue which makes the photoresist widely different in solubility between the pre-exposure to light and the post-exposure. This means that the photoresist layer has a dull edge.
It is possible to overcome those drawbacks by employing copolymerization with certain comonomers for improving the difference in solubility and/or comonomers for enhancing the adhesion to substrates. t-butyl methacrylate and tetrahydropyranyl methacrylate are examples of the comonomer for improving the difference in solubility, and methacrylic acid is an example of the comonomer for enhancing the adhesion to substrates. However, the comonomer is required at least 50 mole %. The comonomer is less resistive against dry etching. Thus, the manufacturers desire new photoresist which exhibits high transparency to the exposure light, large difference in the solubility and strong adhesion to substrates without sacrifice of the resistance against dry etching.
The other sorts of photoresist, which contain the alternating copolymerization between norbornene and maleic anhydride, have the norbornane ring, The norbornane ring also does not have any polar group, and the photoresist exhibits poor adhesion. When copolymer with acrylic acid is introduced into the resin based on the alternating copolymer between norbornene and maleic anhydride, the adhesion is improved. However, the resultant photoresist is less resistive against dry etching. The manufacturers also desire new photoresist exhibiting strong adhesion to substrates without sacrifice of the resistance against dry etching.
It is therefore an important object of the present invention to provide photoresist which exhibits high transparency to light equal in wavelength to or less than 220 nm, large resistance against dry etching and strong adhesion to substrates.
It is another important object of the present invention to provide polymer to be used in the photoresist.
It is yet another important object of the present invention to provide monomer to be used in the polymer.
It is still another important object of the present invention to provide a method for transferring a pattern to the photoresist layer.
The present inventors found that 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl skeleton was useful for photoresist. The present inventors examined documents referring to photoresist having the skeleton. Japanese Patent Application laid-open No. 2001-188351 taught the photoresist having the bridged alicylic skeleton in which at least one ring is lactone ring. Norbornyl monoene, norbornyl diene, tricyclodecamonoene, tricyclodecadiene, tetracyclodecamonoene and tetracyclodecadiene were written in the Japanese Patent Application laid-open as the examples. Japanese Patent Application laid-open No. 2000-26446 taught (meth)acrylate polymer having the bridged lactone structure. However, the present inventors could not find any document teaching that 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl skeleton was useful for photoresist.
In accordance with one aspect of the present invention, there is provided monomer for a chemically amplified photoresist comprising vinyl monomer having 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl group expressed by general formula (1) 
where each of L1, L2, L3, L4, L5 and L6 is selected from the group consisting of hydrogen atom and alkyl groups having the carbon number from 1 to 8.
The hydrogen atom or alkyl group at L5 and the hydrogen atom or alkyl group at L6 may be replaced with alkylene groups having the carbon number 1 to 10 and bonded to each other for forming a ring.
The 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl group expressed by general formula (1) may be replaced with vinyl monomer with a bridged alicylic xcex4 lactone structure expressed by general formula (2) 
where each of R2 and R3 is selected from the group consisting of hydrogen and alkyl groups having the carbon number from 1 to 4, each of R4 to R6 is selected from the group consisting of hydrogen atom and methyl group, R7 and R8 are hydrogen atoms or alkylene groups each having the carbon number from 1 to 10 and bonded for forming a ring and n is zero or 1.
In accordance with another aspect of the present invention, there is provided polymer used for a chemically amplified photoresist comprising vinyl polymer having 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl group expressed by general formula (1) 
where each of L1, L2, L3, L4, L5 and L6 is selected from the group consisting of hydrogen atom and alkyl groups having the carbon number from 1 to 8.
The hydrogen atom or alkyl group at L5 and the hydrogen atom or alkyl group at L6 may be replaced with alkylene groups having the carbon number 1 to 10 and bonded to each other for forming a ring.
The 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl group expressed by general formula (1) may be replaced with vinyl monomer with a bridged alicylic xcex4 lactone structure expressed by general formula (2) 
where each of R2 and R3 is selected from the group consisting of hydrogen and alkyl groups having the carbon number from 1 to 4, each of R4 to R6 is selected from the group consisting of hydrogen atom and methyl group, R7 and R8 are hydrogen atoms or alkylene groups each having the carbon number from 1 to 10 and bonded for forming a ring and n is zero or 1.
In accordance with yet another aspect of the present invention, there is provided photoresist comprising polymer including vinyl polymer having 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl group expressed by general formula (1) 
where each of L1, L2, L3, L4, L5 and L6 is selected from the group consisting of hydrogen atom and alkyl groups having the carbon number from 1 to 8, and photo-acid generator generating acid in the presence of light equal in wavelength to or less than 220 nanometers, the ratio of the photo-acid generator to the photoresist is fallen within the range from 0.2% by mass to 30% by mass.
The hydrogen atom or alkyl group at L5 and the hydrogen atom or alkyl group at L6 may be replaced with alkylene groups having the carbon number 1 to 10 and bonded to each other for forming a ring.
The 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl group expressed by general formula (1) may be replaced with vinyl monomer with a bridged alicylic xcex4 lactone structure expressed by general formula (2) 
where each of R2 and R3 is selected from the group consisting of hydrogen and alkyl groups having the carbon number from 1 to 4, each of R4 to R6 is selected from the group consisting of hydrogen atom and methyl group, R7 and R8 are hydrogen atoms or alkylene groups each having the carbon number from 1 to 10 and bonded for forming a ring and n is zero or 1.
In accordance with still another aspect of the present invention, there is provided a method for transferring a pattern to a photoresist layer, comprising the steps of a) preparing a substrate and photoresist comprising polymer including polymer having 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl group expressed by general formula (1) 
where each of L1, L2, L3, L4, L5 and L6 is selected from the group consisting of hydrogen atom and alkyl groups having the carbon number from 1 to 8 and photo-acid generator generating acid in the presence of light equal in wavelength to or less than 220 nanometers, the ratio of the photo-acid generator to the photoresist being fallen within the range from 0.2% by mass to 30% by mass, b) spreading the photoresist on the substrate for forming a photoresist layer, c) exposing the photoresist layer to image-carrying light having a wavelength between 180 nanometers and 220 nanometers for forming a latent image in the photoresist layer, and d) developing the latent image so as to pattern the photoresist layer into a photoresist patterned layer.
The hydrogen atom or alkyl group at L5 and the hydrogen atom or alkyl group at L6 may be replaced with alkylene groups having the carbon number 1 to 10 and bonded to each other for forming a ring.
The 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl group expressed by general formula (1) may be replaced with vinyl monomer with a bridged alicylic xcex4 lactone structure expressed by general formula (2) 
where each of R2 and R3 is selected from the group consisting of hydrogen and alkyl groups having the carbon number from 1 to 4, each of R4 to R6 is selected from the group consisting of hydrogen atom and methyl group, R7 and R8 are hydrogen atoms or alkylene groups each having the carbon number from 1 to 10 and bonded for forming a ring and n is zero or 1.
The present inventors selected the 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl skeleton from the bridged alicylic xcex4 lactone skeletons for the polymer used for chemically amplified photoresist according to the present invention. The 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl skeleton enhanced the transparency of the chemically amplified photoresist to the light equal in wavelength to or less than 220 nanometers without sacrifice of the resistance against etching and adhesion to substrates. The reasons for the preferable features were as follows.
First, the present inventors discovered that bicyclo[3.2.1]octane skeleton made the photoresist transparent to the light equal in wavelength to or less than 220 nanometers and resistive to dry etching. The reason for the high transparency was that the bridged alicylic structure did not have any aromatic ring. The carbon density was so high that the bridged alicylic structure well withstood the dry etching. Especially, the bicyclo[3.2.1]octane had the molecular structure desirable from the viewpoint of the transparency and the resistance against dry etching. The 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl skeleton included the bicyclo[3.2.1.]octane skeleton so that the photoresist according to the present invention exhibited high transparency without sacrifice of the resistance against the dry etching.
Second, xcex4 lactone ring had the dielectric constant larger in value than that of the ester structure, ether structure and alcohol structure. Referring to xe2x80x9cCHEMICAL HANDBOOK basic IIxe2x80x9d, revised edition 3, pages 502 to 504, edited by Japanese Chemical Society and published by Maruzen Corporation, the dielectric constant of the compounds having the carbon number 4 were as follows. The dielectric constant of xcex3-buthyrolactone was 39, the dielectric constant of ethyl accetate was 6.02, the dielectric constant of diethyl ether was 4.355, and the dielectric constant of 1-butanol was 17.51. Thus, the lactone structure was larger in dielectric constant than the other structures. The large dielectric constant resulted in clear polarity. Especially, the xcex4 lactone exhibited an appropriate value of the dielectric constant. The large dieelctric constant was desirable for adhesion to substrates. The 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl skeleton had the xcex4 lactone ring so that the photoresist according to the present invention achieved strong adhesion to substrates.
The 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl skeleton had both of the bicyclo[3.2.1]octane skeleton and the xcex4 lactone skeleton. This meant that the 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl skeleton was expected to exhibit synergism of the bicyclo[3.2.1]octane skeleton and the xcex4 lactone skeleton. Thus, the 3-oxo-4-oxabicyclo[3.2.1]octane-2-yl skeleton was desirable for the transparency to the light, resistance against dry etching and strong adhesion to substrates.
Monomer and Polymer
Any vinyl monomer is available for the chemically amplified photoresist according to the present invention in so far as the vinyl monomer is active in polymerization. From this viewpoint, it is preferable to use ethylene, a derivative of ethylene, vinyl chloride, a derivative of vinyl chloride, styrene, a derivative of styrene, acrylonitrile, a derivative of acrylonitrile, (meth)acrylate, a derivative of (meth)acrylate, norbornene carboxylic acid ester or a derivative of norbornene carboxylic acid ester for polymer. When the polymer is produced from the ethylene, a derivative of ethylene, vinyl chloride, a derivative of vinyl chloride, styrene, a derivative of styrene, acrylonitrile, a derivative of acrylonitrile, (meth)acrylate, a derivative of (meth)acrylate, norbornene carboxylic acid ester or a derivative of norbornene carboxylic acid ester, the vinyl polymer has repeated structural unit produced through the vinyl polymerization in the principal chain.
More particularly, it is preferable to use the derivatives of (meth)acrylate having the bridged alicylic xcex4 lactone structure expressed by general formula (3) as the structural unit 
where R1 is selected from the group consisting of hydrogen atom and methyl group, each of R2 and R3 is selected from the group consisting of hydrogen atom and alkyl groups having the carbon numbers from 1 to 4, each of R4, R5 and R6 is selected from the group consisting of hydrogen atom and methyl group, R7 and R8 are hydrogen atoms or alkylene groups having the carbon number from 1 to 10 and bonded to each other for forming a ring and n is zero or 1.
When the derivative of (meth)acrylate is vinyl polymerized, the resultant polymer in the acrylic series has the bridged alicylic xcex4 lactone structure expressed by general formula (3xe2x80x2) in the principal chain as the repeated structural unit. 
where R1 is selected from the group consisting of hydrogen atom and methyl group, each of R2 and R3 is selected from the group consisting of hydrogen atom and alkyl groups having the carbon numbers from 1 to 4, each of R4, R5 and R6 is selected from the group consisting of hydrogen atom and methyl group, R7 and R8 are hydrogen atoms or alkylene groups having the carbon number from 1 to 10 and bonded to each other for forming a ring and n is zero or 1.
The derivatives of (meth)acrylate may have alicylic lactone structure expressed by general formula (3xe2x80x3) 
where R1, R4, R5 and R6 are hydrogen atoms or methyl groups, R2 and R3 are hydrogen atoms or alkyl groups having the carbon number from 1 to 4 and R7 and R8 are hydrogen atoms or alkylene groups bonded to each other for forming a ring. When the derivative of (meth)acrylate having the structural unit expressed by general formula (3xe2x80x3) is polymerized, the resultant polymer has the structural unit expressed by general formula (3xe2x80x3xe2x80x2) in the principal chain. 
where R1, R4, R5 and R6 are hydrogen atoms or methyl groups, R2 and R3 are hydrogen atoms or alkyl groups having the carbon number from 1 to 4 and R7 and R8 are hydrogen atoms or alkylene groups bonded to each other for forming a ring. When chemically amplified resist is produced on the basis of the polymer having the structural unit expressed by the general formula (3xe2x80x3xe2x80x2), the chemically amplified resist contains photo-acid generator. It is preferable that the polymer ranges from 70% to 99.8% by mass in the total mass of the polymer and the photo-acid generator.
Derivatives of norbornene carboxylic acid ester are also preferable. The derivatives of norbornene carboxylic acid ester have a bridged alicylic xcex4 lactone structure expressed by general formula (4) 
where R1 is selected from the group consisting of hydrogen atom and methyl group, each of R2 and R3 is selected from the group consisting of hydrogen atom and alkyl groups having the carbon number from 1 to 4, each of R4, R5 and R6 is selected from the group consisting of hydrogen atom and methyl group, R7 and R8 are hydrogen atoms or alkylene groups having the carbon number from 1 to 10 and bonded to each other for forming a ring and n is zero or 1.
When the derivative of norbornene carboxylic acid ester with the bridged alicylic xcex4 lactone structure expressed by general formula (4) is polymerized, the resultant polymer has a bridged alicylic xcex4 lactone structure expressed by general formula (4xe2x80x2) in the principal chain as the repeated structural unit 
where R1 is selected from the group consisting of hydrogen atom and methyl group, each of R2 and R3 is selected from the group consisting of hydrogen atom and alkyl groups having the carbon number from 1 to 4, each of R4, R5 and R6 is selected from the group consisting of hydrogen atom and methyl group, R7 and R8 are hydrogen atoms or alkylene groups having the carbon number from 1 to 10 and bonded to each other for forming a ring and n is zero or 1.
More than one vinyl monomer may be copolymerized. When more than one vinyl monomer is copolymerized, the resultant copolymer has more than one structural unit in the principal chain as the repeated structural unit. Thus, a wide variety of desirable properties are given to the photoresist according to the present invention by using the copolymers.
As described hereinbefore, each of the R1, R4, R5 and R6 is a hydrogen atom or methyl group in the general formulae (2), (3), (4), (3xe2x80x2) and (4xe2x80x2). In those general formulae, each of the R2 and R3 is a hydrogen atom or alkyl group having the carbon number from 1 to 4, i.e., methyl group, ethyl group, n-propyl group and n-butyl. R7 and R8 are hydrogen atoms or alkylene groups, which have the carbon number from 1 to 10 and are bonded to each other for forming a ring. Examples are propylene group [xe2x80x94(CH2)3xe2x80x94], butylene group [xe2x80x94(CH2)4xe2x80x94] and 1,3-cyclopentylene group.
In the general formula (1), L1 is exchangeable for R4, L2 is exchangeable for R5, L3 and L4 are independently exchangeable for R6, L5 is exchangeable for R7, and L6 is exchangeable for R8.
For examples, in case where the derivatives of (meth)acrylate have n equal to 1, following compounds are available for the polymer and, accordingly, photoresist. 
In case where the derivatives of norbornene carboxylic acid ester have n equal to 1, following compounds are available for the polymer and, accordingly, the photoresist. 
In case where the derivatives of (meth)acrylate have n equal to zero, following compounds are available for the polymer and photoresist. 
In case where the derivatives of norbornene carboxylic acid ester have n equal to zero, followings are available for the polymer and the photoresist. 
In addition to the above-described repeated structural unit, comonomer may be copolymerized so as to introduce a repeated structural unit to be decomposed by acid produced from photo-acid generator and/or another repeated structural unit expected to impart various desirable features into the polymer.
The repeated structural units, which are produced from the comonomer, are expected to exhibit a high decomposition efficiency, impart desirable features to the polymer and have good affinity to the vinyl polymerization. From these viewpoints, it is desirable to have at least one of the structural units expressed by the general formulae (3xe2x80x2a), (3xe2x80x2b) and (3xe2x80x2c). 
where R9 is selected from the group consisting of hydrogen atom and methyl group, R10 is selected from the group consisting of groups to be decomposed by acid and bridged cyclic hydrocarbon groups having the carbon number from 7 to 13 and having groups to be decomposed by acid, R11 is selected from the group consisting of hydrogen atom and methyl group, R12 is selected from the group consisting of hydrogen atom, hydrocarbon groups having the carbon number from 1 to 12, bridged cyclic hydrocarbon groups having the carbon number from 7 to 13 and either hydroxy or carboxy group and 2,6-norbornanecarbolactone-5-yl group and M is selected from the group consisting of hydrogen atom, hydroxy group, hydroxyalkyl groups and acid dissociated organic groups having the carbon number equal to or less than 20 and to be decomposed by acid for producing carboxy group.
R10 is the group to be decomposed by acid or the bridged cyclic hydrocarbon groups, which have the carbon number from 7 to 13 and a group to be decomposed by acid. Examples of the group to be decomposed by acid are t-butyl, tetrahydropyran-2-yl group, tetrahydrofuran-2-yl group, 4-methoxytetrahydropyran-4-yl group, 1-ethoxyethyl group, 1-butoxyethyl group, 1-propoxyethyl group, 3-oxocyclohexyl group, 2-methyl-2-adamantyl group, 2-ethyl-2-adamantyl group, 1-methyl-1-adamantylethyl group, 8-methyl-8-tricyclo[5.2.1.02,6]decyl group, 1,2,7,7-tetramethyl-2-norbornyl group, 2-acetoxymentyl group, 2-hydroxymentyl group and 1-methyl-1-cyclohexylethyl group.
Examples of the bridged cyclic hydrocarbon groups having the carbon number from 7 to 13 and a group to be decomposed by acid have ester group, and are tricyclo[5.2.1.02,6]decyl methyl group, tricyclo[5.2.1.02,6]decyl group, adamantyl group, norbornyl group, methylnorbornyl group, isobornyl group, tetracyclo[4.4.0.12,5.17,10]dodecyl group and methyltetracyclo[4.4.0.12,5.17,10]dodecyl group. The chemical structures of these groups are as follows.
In the chemical structures, R17 is the group to be decomposed by acid, and examples of the group are t-butyl, tetrahydropyran-2-yl group, tetrahydrofuran-2-yl group, 4-methoxytetrahydropyran-4-yl group, 1-ethoxyethyl group, 1-butoxyethyl group, 1-propoxyethyl group, 3-oxocyclohexyl group, 2-methyl-2-adamantyl group, 2-ethyl-2-admantyl group, 8-methyl-8-tricyclo[5.2.1.02,6]decyl group, 1,2,7,7-tetramethyl-2-norbornyl group, 2-acetoxymenthyl group, 2-hydroxymenthyl group and 1-methyl-1-cyclohexylethyl group.
In case where R12 is a hydrocarbon group having the carbon number from 1 to 12, examples of R12 are methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, cyclohexyl group, tricyclo[5.2.1.02,6]decyl group, adamantyl group, norbornyl group, isobornyl group and tetracyclo[4.4.0.12,5.17,10]dodecyl group.
Examples of the bridged cyclic hydrocarbon having the carbon number from 7 to 13 and one of the hydroxy group and carboxy group are hydroxyadamantyl group, dihydroxyadamantyl group, hydroxynorbornyl group, hydroxytetracylcododecyl group, carboxyadamantyl group, carboxynorbornyl group and carboxytetracyclododecyl group.
In case where M is hydroxyalkyl group, examples of M are hydroxymethyl group and hydroxyethyl group.
In case where M is the acid dissociated organic group having the carbon number equal to or less than 20 and to be decomposed by acid for producing carboxy group, examples of M are t-butoxycarbonyl group, tetrahydropyranyloxycarbonyl group, tetrahydrofuranyloxycarbonyl group, 4-methoxy tetorahydropyranyloxycarbonyl group, 1-ethoxyethoxycarbonyl group, 1-butoxyethoxycarbonyl group, 1-propoxyethoxycarbonyl group, 3-oxocyclohexyloxycarbonyl group, 2-methyl-2-admantyloxycarbonyl group, 2-ethyl-2-adamantyloxycarbonyl group, 8-methyl-8-tricyclo[5.2.1.02,6]decyloxycarbonyl group, 1,2,7,7-tetramethyl-2-norbornyloxycarbonyl group, 2-acetoxymenthyloxycarbonyl group, 2-hydroxymenthyloxycarbonyl group and 1-methyl-1-cyclohexylethoxycarbonyl group.
Other repeated structural units are expected to enhance the decomposition efficiency and/or give the photoresist other desirable features. Comonomers for these repeated structural units are to be well polymerized for producing vinyl polymer. From this viewpoint, at least one of the structural units expressed by the general formulae (4xe2x80x2a), (4xe2x80x2b) and (4xe2x80x2c) is preferable. 
where R13 is selected from the group consisting of hydrogen atom and methyl group, R14 is selected from the group consisting of hydroxy group, hydroxyalkyl group and acid dissociated organic groups having the carbon number equal to or less than 20 and to be decomposed by acid for producing carboxy group, R15 is selected from the group consisting of hydrogen atom and methyl group and R16 is selected from the group consisting of hydroxy group, hydroxyalkyl group and acid dissociated organic groups having the carbon number equal to or less than 20 and to be decomposed by acid for producing carboxy group.
Each of R14 and R16 is hydroxy group, hydroxyalkyl group such as hydroxymethyl group and hydroxyethyl group or acid dissociated organic groups having the carbon number equal to or less than 20 and to be decomposed by acid for producing carboxy group. The group of acid dissociated organic groups contains t-butoxycarbonyl group, tetrahydropyranyloxycarbonyl group, tetrahydrofuranyloxycarbonyl group, 4-methoxytetrahydropyranyloxycarbonyl group, 1-ethoxyethoxycarbonyl group, 1-butoxyethoxycarbonyl group, 1-propoxyethoxycarbonyl group, 3-oxocyclohyxyloxycarbonyl group, 2-methyl-2-adamantyloxycarbonyl group, 2-ethyl-2-adamantyloxycarbonyl group, 8-methyl-8-tricyclo[5.2.1.02,6]decyloxycarbonyl group, 1,2,7,7-tetramethyl-2-norbornyloxycarbonyl group, 2-acetoxymenthyloxycarbonyl group, 2-hydroxymenthyloxycarbonyl group and 1-methyl-1-cyclohexylethoxycarbonyl group.
From the viewpoint of desirable properties of resultant copolymer, it is preferable to copolymerize each of the repeated structural units expressed by the general formulae (3xe2x80x2a), (3xe2x80x2b) and (3xe2x80x2c) with at least one of the repeated structural unit expressed by the general formulae (4xe2x80x2a), (4xe2x80x2b) and (4xe2x80x2c). It is also preferable to copolymerize each of the repeated structural units expressed by the general formulae (4xe2x80x2a), (4xe2x80x2b) and (4xe2x80x2c) with at least one of the repeated structural unit expressed by the general formulae (3xe2x80x2a), (3xe2x80x2b) and (3xe2x80x2c). The repeated structural units expressed by the general formulae (3xe2x80x2a) to (3xe2x80x2c) may be selectively incorporated in the polymer concurrently with the repeated structural units expressed by the general formulae (4xe2x80x2a) to (4xe2x80x2c) so as to give a wide variety of desirable properties to the polymer.
It is preferable that the copolymer contains at least one of the repeated structural units expressed by the general formulae (3xe2x80x2) and (4xe2x80x2) fallen within the range between 5 mole % and 90 mole % from the viewpoint of the properties of the resultant polymer. It is more preferable that at least one of the repeated structural units expressed by the general formulae (3xe2x80x2) and (4xe2x80x2) is fallen within the range between 7 mole % and 80 mole %. It is much more preferable that at least one of the repeated structural units expressed by the general formulae (3xe2x80x2) and (4xe2x80x2) is fallen within the range between 10 mole % and 70 mole %.
Since the repeated structural units expressed by the general formulae (3xe2x80x2a) to (3xe2x80x2c) well react with the derivatives of (meth)acrylate expressed by the general formula (3), it is preferable to make the repeated structural unit or units expressed by the general formulae (3xe2x80x2a) to (3xe2x80x2c) copolymerized with the repeated structural unit expressed by the general formula (3xe2x80x2). In this instance, it is preferable that the structural unit expressed by general formula (3xe2x80x2) is fallen within the range between 5 mole % and 90 mole % of the copolymer. It is more preferable that the structural unit expressed by general formula (3xe2x80x2) is fallen within the range between 7 mole % and 80 mole % of the copolymer. It is much more preferable that the structural unit expressed by general formula (3xe2x80x2) is fallen within the range between 10 mole % and 70 mole % of the copolymer.
Since the repeated structural units expressed by the general formulae (4xe2x80x2a) to (4xe2x80x2c) well react with the derivatives of norbornene carboxylic acid ester expressed by the general formula (4), it is preferable to make the repeated structural unit or units expressed by the general formulae (4xe2x80x2a) to (4xe2x80x2c) copolymerized with the repeated structural unit expressed by the general formula (4xe2x80x2). In this instance, it is preferable that the structural unit expressed by general formula (4xe2x80x2) is fallen within the range between 5 mole % and 90 mole % of the copolymer. It is more preferable that the structural unit expressed by general formula (4xe2x80x2) is fallen within the range between 7 mole % and 80 mole % of the copolymer. It is much more preferable that the structural unit expressed by general formula (4xe2x80x2) is fallen within the range between 10 mole % and 70 mole % of the copolymer.
The polymers described hereinbefore are produced through a usual polymerization process such as, for example, the radical polymerization, anionic polymerization or addition polymerization. A suitable polymerization initiator such as, for example, azobisisobutyronitrile (AIBN) is, by way of example, added to dry tetrahydrofuran in inert atmosphere such as argon or nitrogen, and the polymerization initiator and the dry tetrahydrofuran are agitated at 50 degrees to 70 degrees in centigrade for 0.5 hour to 12 hours. Then, the polymer is produced through the radical polymerization.
In case where the polymer is produced through the addition polymerization, the polymer may be produced through the process disclosed by J. P. Mathew, Macromolecules, vol. 29, pages 2755 to 2763, 1996. Namely, suitable catalyst in palladium compound series is used in the addition polymerization. (xcex73-allyl)Pd(BF4), (xcex73-allyl)Pd(SbF6) and [Pd(CH3CN)4](BF4)2 are examples of the palladium compound catalyst. Otherwise, nickel compound catalyst such as bis (pentafluorophenyl) nickel toluene complex is used in the addition polymerization as taught by T. Chiba et. al, Journal of Photopolymer Science and Technology, vol. 13, No. 4, pages 657 to 664, 2000.
The weight average molecular weight of the polymer available for the photoresist according to the present invention is fallen within the range from 2,000 to 200,000.
Chemically Amplified Resist
Chemically amplified resist embodying the present invention contains at least the polymer described hereinbefore and photo-acid generator. In case where n and both of R2 and R3 are 1 and alkyl group in the structural unit expressed by the general formula (3xe2x80x2), the alicylic lactone unit is a tertiary ester of carboxylic acid, and is eliminated in the presence of acid. Thus, it is an acid decomposed group. The reaction is as follows. 
It is preferable that the photo-acid generator generates acid in the presence of the light equal in wavelength to or less than 400 nanometers. It is more preferable to produce the acid in the presence of the light having the wavelength between 180 nanometers and 220 nanometers. There is not any limit to the photo-acid generator in so far as liquid mixture, in which the mixture containing the photo-acid generator and the polymer such as the polymer in acrylic series is well dissolved in organic solvent, is uniformly spread by using a spin coater, by way of example. More than one photo-acid generator may be mixed with the polymer.
Examples of the photo-acid generator are derivatives of triphenylsulfonium salt, derivatives of diphenyliodonium salt, derivatives of dialkylphenacylsulfonium salt, derivatives of nitrobenzylsulfonate and derivatives of sulfonic acid ester of N-hydroxysuccinimide.
Another photo-acid generator is disclosed by J. V. Crivello et. al, Journal of the Organic Chemistry, vol. 43, No. 15, pages 3055 to 3058, 1978. J. V. Crivello et. al. teach derivatives of triphenylsulfonium salt and other onium salts such as sulfonium salt, iodonium salt, phosphonium salt, diazonium salt and ammonium salt. Yet another photo-acid generator is disclosed by O. Nalamasu et. al, SPIE Proceedings, vol. 1262, page 32, 1990. O. Nalamasu et. al. teach 2,6-dinitrobenzyl esters. Still another photo-acid generator is disclosed by Takumi Ueno et. al, Proceedings of PME"" 89, Kohdansha, pages 413 to 424, 1990, and Ueno et. al. teach 1,2,3-tri(methanesulfonyloxy)benzen. Yet another photo-acid generator is disclosed in Japanese Patent Application laid-open No. 5-134416, and is sulfosuccinimide.
From the viewpoint that the photo-acid generator makes the chemically amplified resist well sensitive to the exposure light for producing a fine latent image therein, it is preferable that the content of the photo-acid generator is equal to or greater than 0.2% by mass of both polymer and photo-acid generator. It is more preferable that the chemically amplified resist contains the photo-acid generator equal to or greater than 1% by mass of both polymer and photo-acid generator. However, if the content of photo-acid generator is greater than 30% by mass, the chemically amplified resist is less liable to be uniformly spread, and the scum is not ignorable after the development. Thus, the upper limit of the content is 30% by mass. It is more preferable that the content of the photo-acid generator is equal to or less than 15% by mass. Thus, the photo-acid generator is to range from 0.2% by mass to 30% by mass, and the more preferable range is between 1% by mass and 15% by mass.
When the manufacturer prepares the chemically amplified resist, appropriate solvent is used. Any organic solvent is available for the chemically amplified resist in so far as the polymer and the photo-acid generator are well dissolved therein for being uniformly spread over substrates. Only one sort of solvent or more than one sort of solvent is used for preparing the chemically amplified resist according to the present invention.
Examples of the solvent are n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, tert-butyl alcohol, propylene glycol monomethylether acetate, propylene glycol monoethylether acetate, methyl cellosolve acetate, ethyl cellosolve acetate, ethyl lactate, methyl lactate, 2-methoxybutyl acetate, 2-ethoxyethyl acetate, methyl, pyruvate, ethyl pyruvate, 3-methoxy methyl propionate, 3-methoxy ethyl propionate, N-methyl-2-pyrrolidinone, cyclohexanone, cyclopentanone, cyclohexanol, methyl ethyl ketone, 1,4-dioxane, ethyleneglycolmonomethylether, ethyleneglycolmonomethylether acetate, ethyleneglycolmonoethylether, ethyleneglycolmonoisopropylether, diethyleneglycolmonomethylether and diethyleneglicoldimethylether.
The chemically amplified resist according to the present invention may further contain other additives such as, for example, dissolution inhibitor, organic base, surface active agent, dyestuff, stabilizer, coating property improving agent and coloring agent.
Pattern Transfer
A pattern image is transferred from a photo-mask to a chemically amplified resist layer as follows. First, the chemically amplified resist described hereinbefore is prepared. The chemically amplified resist solution is spread over a layer such as, for example, a semiconductor wafer or a semiconductor/insulating layer on the semiconductor wafer. A spin coater may be used for spreading the chemically amplified resist solution.
Subsequently, the chemically amplified resist layer is pre-baked, and, thereafter, the semiconductor wafer is inserted into a chamber of an aligner. The aligner is well known to skilled person, and no further description is hereinbelow incorporated. Laser light is radiated from a light source to a photo-mask. The laser light has the wavelength between 180 nanometers and 220 nanometers. In this instance, the light source radiates 193 nanometer wavelength ArF excimer laser light. The ArF excimer laser light passes through the photo-mask, and carries the pattern image on the photo-mask. The image-carrying light reaches the chemically amplified resist layer. The image-carrying light produces a latent image in the chemically amplified resist layer.
The semiconductor wafer is taken out from the aligner, and the latent image is developed. Then, the chemically amplified resist layer is patterned into a resist mask. Using the resist mask, the semiconductor/insulating layer is, by way of example, selectively etched. Otherwise, dopant impurity may be ion implanted into the semiconductor/insulting layer or semiconductor wafer. Thus, the semiconductor device manufactures form miniature patterns on or over the semiconductor wafers.
Description is hereinbelow made on several examples. However, these examples do not set any limit to the scope of the present invention. High-purity reagents and other chemicals used in the examples were purchased in the market. However, when special reagent or chemical was used, the special reagent/chemical is detailed.